| 摘要 |
528,403. Impedance networks. SIEMENS BROS. & CO., Ltd., and REED, M. May 5, 1939, No. 13528. [Class 40 (iii)] In a separator comprising a number of bandpass filters A, B ... N having their input or output terminals connected in parallel, the individual filters are so designed that, over the complete working range of the separator, the impedance as seen from the common terminals is equivalent to a constant resistance shunted by a constant capacity. The insertion of a suitable four-terminal correcting network CN in the common input or output circuit brings the impedance of the whole to a constant resistance. The separator is suitable for selecting different harmonic frequencies produced by a single generator, and each band-pass filter comprises one or more T-sections of the kind shown, or with the series and shunt arms interchanged. In certain cases when the frequencies are high enough, equivalent quartz crystal arrangements may be used. The Specification explains how the filters are designed so that all have the same image impedance in their respective pass ranges and so that the image impedance of each filter outside its pass range is equivalent to a constant capacity. The impedance as seen from the common terminals is then that of a resistance R shunted by a capacity C. The correcting network CN is designed as a band-pass filter (Fig. 1) or as a low-pass filter (Figs. 2, 3) presenting a constant resistance equal to R over the working range, but the shunt capacity CP is made less than the calculated value by the amount C.
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